Process for the purification of mononitro aromatic compounds



Patented Nov. 4, 1947 PROCESS FOR THE PU RIFICATIONOF MONONITRO AROMATIC CGMPOUNDS' William P. Gage, San Anselmo, Calif., assignor to Shell 1 Development Company, San Francisco, Calif.,. a corporation of Delaware No- Drawing.

n 12 Claims. 1

This: invent-ion relates to the purification of mononitro aromatic compounds. It relates particularly toaprocessfor thetreatment of impure mononitro aromatic compounds for the purpose of-refining the sameandzremoving therefromobje'ctionable and difiicultly-removable dinitro aromade-compounds.

The-invention provides a commercially attractivetandhighly effective method for refining crude mononitro aromatic compounds and mixtures thereof" which are unsuitable for: use in many commercial processes for'the reason that they contain varying amounts of dinitro aromatic compounds which are very difl'icult and, in some cases-,- impossible toremove by ordinary methods, as'by distillation; The process of the invention is applicable with excellent results-to the removal of objectionable and difficultly-removable dinitro aromatic compounds from the mononitro aromaticcompounds obtained by effecting the nitrationof the corresponding aromatic hydrocarbons.

The process of theinvention comprises treating an impure mononitro aromatic compound which is :eontam-inatedwith dinitro aromatic compounds with a reducing agent at a temperature and for a time sllfiicient to selectively reduce the said dinitro aromatic compounds to the corresponding aminonitroaromatic compounds without substantial reduction of the mononitro aromatic compounds. Thisforms a mixture comprising themononitro aromatic compounds together with the aminonitroaromatic compounds to which the'aromatic dinitro compounds in the original mixture have been-converted; Theaminonitro aromatic compoundsmay thenbe-separated from the desired mononitro aromatic compounds, and thus leave thelatter in a relatively pure state and in a form suitable for use in the manufacture of other organic compounds; as is more fully'described hereinbelow.

The-process of the invention is of particular value-as applied totheremoval of dinitro aromaticrcom-pounds frommononitro aromatic compounds. prepared by the-direct nitration of the corresponding, aromatic hydrocarbon, e. g. by treating the said. aromatic hydrocarbon with a nitrating mixture" which. may comprise, for example a mixture of suitable quantities of nitric and sulfuric acids. Nitration-of aromatic hydrocarbons by this method produces substantial quantities of dinitroaromatic compounds in addition totherdesired monon'itro derivative. Compiste separation; of the dinitro derivatives from the mononitro aromatic hydrocarbon is extremely difficult; if not'i-mpossible', by use of the ordinary Application November 10, 1943. Serial No. 509,954

methodsyasiby fractional distillation. It'is important for manyindustrial. applications, however thatthe-mononitroaromatic compound be substantially freefromthe dinitro derivative. An example of this is shown inthe following.

Aromatic amines are customarily produced on a commercial-scaleby the reduction of the corresponding aromatic-nitro compounds. Reducing agents commonly used for. this purpose have been, for example, ironand acetic-acid, ironand steam in the presence of small amounts of an acid, zinc'and hydrochloricacid, tin or stannous chloride and hydrochloric acid, and the like. The reduction has alsobeen carriedout by electrolytic processes. Obviously whenxaromatic mononitro compounds" which are" contaminated with aromatic dinitro compounds are used as starting materials for the synthesisof aromatic amines via reductionofthe corresponding nitro compounds, the product will be contaminated by small amounts of aromatic'diamines. These are very difficult to separate: from: thedesired monoamino compounds and their presence even in' small amounts is,.in' some instances, very undesirable. For example; the presence of small amounts of phenylene'diamine's in xylidines, which are widely used as addition agentsinaviation gasoline, may render'the'xylidines unfit for'usefor this purpose. Ihis is becausethe presen'ce of small quantities of phenylen'ediamine impurities has a markedly deleterious effect on the performance ofaviation gasoline in which the xylidines' have been incorporatedas'blending" agents, in that they cause raising of the 'freezin'gpoint of the finished gasoline beyond'acceptab'le limits; In fact, only from about 1% to about- 2% of'the'phenylene diamines can be tolerated in the added xylidines if a freezing' point of C'. is'to'be realized in the finished gasoline.

A further disadvantage: resulting from the presence of 'dinitro compounds as contaminants in. the aromatic mononitro compounds is to be found in the fact th'atthe presence of the said dinitro compounds in the 'nitrated product makes "itdifficult oreven impossible to apply commercial catalytic hydrogenation equipment and procedures'to the reduction of the nitro compounds to the corresponding amines; As is well known many of the dinitro aromatic compounds are highly-explosive in natureand tend to cause seriousexp'losion" when. they, or mixtures containing them, are subjected to the action of hydrogen in the presence of a cat'alyst'under the conditions customarily employed in commercial catalytic hydrogenation equipment. This may be 3 true even though the feed stock contains but small amounts of dinitro aromatic compounds, since the latter tend to accumulate as a condensate or dew in cool parts of the reactor or in pipe threads, etc., so as to be present in dangerous concentrations. The explosive natureof these compounds thus places a serious limitation on the process outlined hereinabove for the manufacture of amino aromatic compounds, particularly the xylidines, in that it makes it difficult, if not impossible, to use technical grade mononitro aromatic compounds which are contaminated with dinitro aromatic hydrocarbons as starting materials for the synthesis of the corresponding aromatic monoamines via catalytic reduction in available equipment and using standard procedures.

Hitherto no practical and economical method has been proposed for effecting a thorough and economical separation of dinitro aromatic hydrocarbons from mononitro aromatic hydrocarbons. As pointed out hereinabove, this has made it impossible to use large scale continuous catalytic hydrogenation equipment for the reduction of technical mononitro aromatic hydrocarbons without undue danger of explosion, thereby making it necessary to resort to relatively tedious, uneconomical and relatively inefficient small scale operations for the reduction of the mononitro aromatic compounds.

The present invention provides a simple but effective process for purifying the technical grade mononitro aromatic compounds obtained by the nitration of the corresponding aromatic hydrocarbons. It also provides an economical method for thoroughly removing any dinitro aromatic hydrocarbons which may be present as contaminating materials, thereby making it possible to use the said aromatic mononitro compounds in a wide variety of chemical processes without danger of explosion. Specifically, it affords a practical and efiective procedure for the separation of mononitro xylenes from small but dangerous amounts of dinitro xylenes so as to form a product comprising substantially pure mononitro xylenes which may be reduced with safety to the corresponding xylidines in large scale commercial hydrogenation equipment without the formation of diamino xylenes in such amounts as to make the xylidines unsuited for use as blending agents in aviation gasoline.

The process of the invention essentially comprises purifying a crude mononitro aromatic hydrocarbon and rendering it free from objectionable impurities comprising the corresponding dinitro aromatic compounds by subjecting it to the action of a selective reducing agent under conditions such as to effect the selective reduction of the dinitro aromatic compounds to the corresponding aromatic nitroamines without substantial reduction of the mononitro aromatic compounds, and separating the thus formed aromatic nitroamines from the unchanged mononitro aromatic compounds. This selective reduction may be effected by procedures in which a variety of reducing agents and operating conditions are employed, all of which procedures are within the scope of the invention.

In one embodiment of the invention a technical mononitro aromatic compound formed by the nitration of the corresponding aromatic hydrocarbon and comprising largely mononitro aromatic compounds together with lesser amounts of dinitro aromatic compounds is treated with an aqueous solution of a. I I QUV? reducing agent, e. g. sodium disulfide, ammonium sulfide and the like, so as to selectively reduce but one nitro group of the dinitro aromatic compound and form the corresponding aminonitro aromatic compound without substantial reduction of the nitro group of the mononitro aromatic compound. This forms a reaction mixture containing the unreacted mononitro aromatic compound together with lesser amounts of aromatic nitroamines, which may then be separated from the said mononitro aromatic compound, leaving the latter in a substantially pure form so that it is suitable for use as a raw material for the preparation of other valuable compounds, especially the corresponding aromatic amines. The procedure as outlined thus provides a safe and effective method for separatingthe undesirable dinitro compounds formed concurrently with the mononitro compounds during the nitration of an aromatic hydrocarbon since the dinitro derivatives may be converted by selective reduction with a mild reducing agent such as sodium disulfide or ammonium sulfide to form an aromatic nitroamine, while the mononitro derivative is not appreciably affected by the treatment.

The aminonitro aromatic compound may be separated from the mononitro aromatic compound in any desired manner, as by distillation. However, since the said aromatic nitroamine formed by the described selective reduction step contains a group which is basic in nature, i. e. the amino group, it may be effectively and easily separated from a neutral compound such as the desired mononitro aromatic compound by washing or extracting a mixture of the two with a dilute acid in which the aromatic nitroamine will be selectively dissolved. It is thus possible to effect the separation of the two types of compounds in the presence of a diluent such as water and without the use of high temperatures or other conditions which might cause the explosion of the relatively sensitive dinitro compound. Removal of the dinitro compounds in this manner also effects another object of the invention in that it results in the formation of a mononitro fraction comprising a mononitro aromatic compound relatively free from dinitro compounds. The said fraction may therefore be handled and subjected to subsequent treatment, e. g. catalytic hydrogenation, without special precautions being taken and without the danger of serious explosions occurring. Since the fraction contains almost no dinitro compounds, it follows as a matter of course that the product resulting from hydrogenation of the said fraction will be relatively free from the diamino compounds which would result from the reduction of the dinitro compounds, and which would make the said fraction unsuitable for incorporation into aviation gasoline blends.

In a preferred embodiment of the invention, a mixture of nitroxylenes which has been prepared by treating commercial xylene with a nitrating reagent comprising a mixture of nitric and sulfuric acids under conditions such as to effect the nitration of the said Xylene and which contains from about to about of mononitroxylene and from about 15% to about 5% of dinitroxylene may be placed in a suitable reaction vessel and mixed with a 10% to 20% solution of sodium disulfide prepared, for example, by dissolving in an aqueous solution of commercial sodium sulfide the theoretical amount of elementary sulfur necessary to convert the sodium sulfide content of the said aqueous solution to sodium disulfide.

Bulficient sodium disulfide solution should be used to introduce into the reaction mixture an amount of sodium .disulfide .slightly in excess of that theoretically required to effect the selective reduction of the dinitro xylenes to nitroamlno fxylenes. After addition of the sodium disulfide solution, the reaction mixture may be-stirred with heating until the reaction is complete. The reaction mixture may then be cooled and the organic layer which contains the mixture of nitroxylenes and aminonitroxylenes separated, washed with water, and extracted with acid, e. g. 6 N hydrochloric acid, to remove the aminonitroxylenes. Two or more extractions with acid may be required .to completely remove the amino.- ni-troxylenes, The mono-nitroxylenes, which are largely unaffected by the acid treatment, :may then be purified by distillation and reduced to the desired xylidines by any suitable means, pref- .erably by treatment with hydrogen in the presence of a catalyst. The aminonitroxylenes which are dissolved in the acid solution may be recovered by neutralization of the acid solution with an alkali, thereby forming a water insoluble .layer containing aminonitroxylenes, separating the said water insoluble layer, and distilling it to isolate and purify the aminonitroxylenes.

Although the foregoing represents a preferred method for preparing amines in accordance with the process of the present invention, the "ma- :terials, conditions and procedures described may be varied or modified to meet the requirements of each particular application. The process of the invention may be applied with suitable modificaticns, .for example, to the separation of the monoand 'di-nitro derivatives of a wide range of aromatic compounds. Although it is particularly well suited to the separation of monoand di-nitro xylenes, it may, in general, be applied to the separation of .monoand di-n'itro derivatives of any aromatic compound having non-intenfering substituent groups. Suitable aromatic compounds are, for example, the monoand dinitro derivatives of benzene, the alkyl benzenes including toluene, diethyl benzene, methyl ethyl benzene, the trimethyl benzenes and the like; the monoand di-nitro derivatives of aromatic hydrocarbons having unsaturated side chains; some monoand di-nitro phenols; some mono- .and -di-nitro aromatic halogen compounds; the

monoand di-nitro derivatives of the aromatic others; and many others.

The reducing agents which may be used in the reduction step must obviously be of such a selective nature as to effect the reduction of .but one I .nitro group of the di-nitro compound so as to form the corresponding aminonitro compound without any appreciable reduction of the other nitro group of the dinitro compound or of the .nitro group of the mononitro compound. Although a number of reducing agents are suitable for this purpose, the sulfide reducing agents com stitute an especially appropriate group. These include the sulfides, disuliides, polysulfides or hydrosul-fidesof ammonium, of the alkali metals, and I fide, calcium polysulfide, ferrous sulfide, 'manganous sulfide and zinc sulfide. Because of its efficiency and availability, sodium disulfide has been found to be a particularly desirable reagent touse for this purpose. The sodium disulfide may advantageously be used asin the form of a 10% :to 20% aqueous solution prepared by dissolving the theoretical amount of sulfur in an aqueous solu' tion of commercial sodium sulfide. When the resulting reagent is contacted with a mixture of monoand di-nitro aromatic hydrocarbons, .at moderately elevated temperatures, the dinitro compound is converted in good yields to the arcmatic .nitroam'ine, while the mononitro compound is substantially unafiected.

The operating conditions under which the re duction step is carried out must, in general, be

such as to favor the reduction :of but one of the.

nitro groups of the dinitro aromatic compound. The necessary mild conditions may usually .be realized by effecting the reduction in alkaline solution, at relatively low temperatures, and with relatively short reaction times. The reducing solution may be made alkaline by the use of an alkaline sulfide reducing :agent, e. g. sodium disulfide. or by the addition of a suitable basic substance, e. ,g. sodium hydroxide, or both. Although the temperature to be employed will be determined in each particular case upon such factors as the nature of the materials being processed and the reducing agent employed, it is in most cases preferred to carry out the reduction at temperatures :of from about C. to about C.

The reaction maybe carried out in any suitable type of apparatus designed for either batch or continuous :operation. .It is generally desirable to agitate the reaction mixture by stirring, shaklog, or other suitable means in order to insure intimate contact between the reducing agent and the mixture of monoand idi-nitro aromatic compounds. Any suitable means may be used for securing such agitation and any type of suitable apparatus may be "used for carrying out the reaction. vMeans maybe provided for recycling any "unreacted 'dinitro compounds back to the reaction chamber for further treatment, if desired.

In general, the selective reduction of the dinitro aromatic compounds may be carried-out at atmospheric pressure. However, subatmospheric or superatmospheric pressures may be used, if desired or necessary because of the nature of the reacting substances.

Separation of the-aromatic nitroamine rromthe unchanged mononitro aromatic compound is preferably accomplished by washing or contacting the mixture resulting from the aforementioned partial reduction step with an acid which is sufficiently strong to react with the aromatic nitroamine to form a water soluble salt and which will not otherwise react with the components of the reaction mixture :so as to :form undesirable byproducts. The stronger mineral acids, e. g. acids selected from the group consisting of hydrochloric acid, hydrobromic acid, sulfuric acid and the phosphoric acids, in appropriate concentrations, are suitable for this purpose. The effective con.- centration range will usually vary between 2 N :and 1B preferably between about 4 N and 8 N. About 62N hydrochloric acid has been ioundto be a particularly .efiective and desirable extracting agent. In most :cases it is desirable to treat the reaction mixture with the acid two or more times in order to insure that the aromatic nitroamines are completely removed. In cases where the arcmatic nitroamide is not readily soluble in acid, itimay also be desirable or necessary to heat the 7 reaction mixture or the acid solution or both before carrying out the extraction.

As has been emphasized hereinabove, one of the chief advantages of the process of the present invention resides in the fact that it results in the formation of mononitro aromatic compounds which may be safely used as raw materials for the preparation of the corresponding aromatic amines by catalytic hydrogenation in large scale, readily available catalytic hydrogenation apparatus. Since the mononitro compounds have been rendered relatively free from explosive dinitro compounds, high pressure and/or high temperature catalytic hydrogenation apparatus and methods may be used with safety and resultant efiiciency. Any of a large number of vapor phase hydrogenation processes may therefore be used, thus making possible the use of existing hydrogenation equipment and the economical production of high yields of aromatic amines. In fact, it has been found that yields of as high as 95% of xylidine may be obtained without hazard by the catalytic reduction of nitroxylene at temperatures ranging from about 100 C. to about 350 C. and pressures of up to 600 pounds per square inch using as hydrogenation catalysts such materials as nickel, granular molybdenum sulfide, iron polysulfide, nickel sulfide, co-precipitated cobalt polysulfide and aluminum hydroxide, mixtures of molybdenum sulfide and tungsten sulfide, iron sulfide-ammonium sulfide aggregates and the like. A articularly efiicient and desirable method for reducing the nitroaromatics to the corresponding aromatic amines comprises treating the redistilled mononitro aromatic compound with hydrogen in a standard reactor at temperatures of between about 275 C. and 300 C., at a pressure of about 70 pounds per square inch, and using a catalyst comprising nickel supported on majolica chips. When applying this method to the reduction of mononitroxylenes, conversions of mononitroxylene to diamine-free xylidine of Well over 95% may be consistently obtained, if the mononitro xylenes used as a starting material have been made relatively free from dinitro xylenes by the process disclosed herein.

The following example in which the amounts of the reacting materials are given in parts by weight illustrates the process of the invention.

Example About 3 parts of technical mononitroxylene which contained about 12% of dinitroxylenes was treated for about 1% hours with about 5 parts of a 14% aqueous solution of sodium disulfide at a temperature of 85 C. to 90 C. At the end of the reaction period the organic layer was separated while the mixture was still hot and extracted three times with about 3 parts of hot 6 N hydrochloric acid to remove the nitroamino compounds. Analysis of the extracted material showed that all but about 27% of the dinitro compounds which were present in the original mixture had been removed by this procedure. The mononitroxylenes were unaffected.

I claim as my invention:

1. A process for the removal of dinitroxylenes from mixtures containing minor amounts thereof with mononitroxylenes which comprises treating the mixture in the liquid phase under alkaline conditions with an aqueous solution of sodium disulfide which contains from about 12% to about 15% by weight of sodium disulfide in an amount in excess of that theoretically required to reduce said dinitroxylene to the corresponding aminonilJrOXylene at a temperature of from about C. to about C. for about 1% hours to selectively reduce the dinitroxylenes to the corresponding amino-nitroxylenes without substantial reduction of the mononitroxylenes, and treating the resulting mixture of mononitroxylenes and amino-nitroxylenes with hydrochloric acid to separate the amino-nitroxylenes therefrom.

2. A process for the purification of a crude mononitroxylene which contains a relatively small amount of dinitroxylene which comprises treating the crude mononitroxylene in the liquid phase with an aqueous solution of sodium disulfide of about 10% to about 20% concentration in an amount in excess of that theoretically required to reduce said dinitroxylene to the corresponding amino-nitroxylene at a temperature of from about 90 C. to about 100 C. for about 1% hours to selectively reduce the dinitroxylene to aminonitroxylene without substantially reducing the mononitroxylene, and separating the resulting amino-nitroxylene from the mononitroxylene by extraction with a strong mineral acid.

3. A rocess for the purification of a mononitroxylene which contains a relatively small amount of dinitroxylene which comprises treating the mononitroxylene in the liquid phase with an aqueous solution of sodium disulfide of about 10% to about 20% concentration in an amount in excess of that theoretically required to reduce said dinitroxylene to the corresponding amino-nitroxylene at a temperature of from about 90 C. to about 100 C, for a period of time sufiicient to selectively reduce the dinitroxylene to aminonitroxy1ene without substantially reducing the mononitroxylene, and separating the resulting amino-nitroxylene from the mononitroxylene by treating with a mineral acid which will form soluble salts by reaction with the said amino-nitroxylene without otherwise reacting therewith.

4. A process for purifying a mononitroxylene which contains a relatively small amount of the corresponding dinitroxylene which comprises treating the mononitroxylene in the liquid phase with a selective reducing agent comprising sodium disulfide at a temperature of about 90 C. to about 100 C. and for a time sufficient to selectively reduce the dinitroxylene to amino-nitroxylene without substantial reduction of the mononitroxylene, nd extracting the resulting amino-nitroxylene from the mononitroxylene with an acid solution. I

5. A process for purifying a mononitroxylene which contains a relatively small amount of the corresponding dinitroxylene which comprises treating the mononitroxylene in the liquid phase under alkaline conditions with a selective reducing agent comprising calcium sulfide of about 10% to about 20% concentration in an amount in excess of that theoretically required to reduce said dinitroxylene to the corresponding amino-nitroxylene at a temperature of about 90 C. to about 100 Cqand for a time sufficient to selectively reduce the dinitroxylene to amino-nitroxylene without substantial reduction of the mononitroxylene, and extracting the resulting amino-nitroxylene from the mononitroxylene with an acid solution.

6. A process for purifying a mononitroxylene' which contains a relatively small amount of the corresponding dinitroxylene which comprises treating the mononitroxylene in the liquid phase under alkaline conditions with a selective reducing agent comprising ammonium sulfide of about to about concentration in an amount in excess of that theoretically required to reduce said dinitroxylene to the corresponding amino-nitroxylene at a temperature of about 90 C. to about 100 C. and for a time sufiicient to selectively reduce the dinitroxylene to amino-nitroxylene without substantiall reduction of the mononitroxylene, and extracting the resulting amino-nitroxylene from the mononitroxylene with an acid solution.

7. A process for the removal of dinitro aromatic hydrocarbons of the monobenzene series having the nitro groups attached to the benzene ring from mixtures containing minor amounts thereof with the corresponding mononitro aromatic hydrocarbons which comprises contacting the mixture in the liquid phase with an aqueous solution of sodium disulfide reducing agent of about 10% to about 20% concentration in an amount in excess of that required to reduce said dinitro compounds to the corresponding aromatic nitroamines at a temperature of about 90 C. to about 100 C. for about 1% hours to selectively reduce the dinitro aromatic hydrocarbons to the corresponding aromatic nitroamines without substantial reduction of the mononitro aromatic hydrocarbons while maintaining alkaline conditions in the reaction mixture, and treating the resulting mixture of mononitro aromatic hydrocarbons and aromatic nitroamines with a strong mineral acid to separate the aromatic nitroamines therefrom.

8. A process for the removal of dinitro aromatic hydrocarbons of the monobenzene series having the nitro groups attached to the benzene ring from mixtures containing minor amounts thereof with the corresponding mononitro aromatic hydrocarbons which comprises contacting the mixture in the liquid phase with an aqueous solution of a sulfide reducing agent of about 10% to about 20% concentration in an amount in excess of that required to reduce said dinitro compounds to the corresponding aromatic nitroamines at a temperature of about 90 C. to about 100 C. and for a time suificient to selectively reduce the dinitro aromatic hydrocarbons to the corresponding aromatic nitroamines without substantial reduction of the mononitro aromatic hydrocarbons while maintaining alkaline conditions in the reaction mixture, and treating the resulting mixture of mononitro aromatic hydrocarbons and aromatic nitroamines with a mineral acid of sufiicient strength to form soluble salts by reaction with the said aromatic nitroamines without otherwise reacting therewith.

9. A process for separating dinitro aromatic hydrocarbons of the monobenzene series having the nitro groups attached to the benzene ring from mixtures containing minor amounts thereof with the corresponding mononitro aromatic hydrocarbons which comprises treating the mixture in the liquid phase with a sulfide reducing agent to selectively reduce the dinitro aromatic hydrocarbons to the corresponding aromatic nitroamines without substantial reduction of the mononitro aromatic hydrocarbons, and extracting the resulting aromatic nitroamines from the 10 corresponding mononitrohydrocarbons with an acid solution.

10. A process for the removal of dinitro aromatic hydrocarbons of the monobenzene series having the nitro groups attached to the benzene ring from mixtures containing minor amounts thereof with mononitro aromatic hydrocarbons of the monobenzene series which comprises treating the mixture under alkaline conditions with a sulphide reducing agent in an amount slightly in excess of that required to reduce said dinitro content to the corresponding amino-nitro compound to selectively reduce the dinitro aromatic hydrocarbons to the corresponding amino-nitro aromatic hydrocarbons Without substantial reduction of the mononitro aromatic hydrocarbons, and extracting the resulting amino-nitro aromatic hydrocarbons from the mononitro aromatic hydrocarbons with an acid solution.

11. In a process of preparing pure mononitroxylenes from a mixture of mononitroxylenes and a relatively small amount of dinitroxylenes obtained by the nitration of xylene, the steps of contacting the mixture in the liquid phase with sodium sulfide in an amount slightly in excess of that required to reduce said dinitro content to the corresponding amino-nitro compound at a temperature of about C. to about C. and for a time sufiicient to selectively reduce the dinitroxylenes to the corresponding amino-nitroxylenes without substantial reduction of the mononitroxylenes and separating said amino-nitroxylenes from the unreacted mononitroxylene.

12. In a process of preparing substantially pure mononitroxylenes from a mixture of mononitroxylenes and a relatively small amount of dinitroxylenes obtained by the nitration of xylene, the steps of treating th said mixture with an aqueous solution of sodium disulfide of about 10% to about 20% concentration in an amount in excess of that theoretically required to reduce said dinitroxylene to the corresponding amino-nitroxylene at a temperature of from about 90 C. to about 100 C. and for about 1% hours to selectively reduce the dinitroxylenes to the corresponding amino-nitroxylenes without substantial reduction of the mononitroxylenes and separating said amino-nitroxylenes from the unreacted mononitroxylene.

WILLIAM P. GAGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 714,428 Wirth Nov. 2, 1902 1,074,545 Flurscheim Sept. 30, 1913 1,662,421 Herold Mar. 13, 1928 1,673,154 Miller June 12, 1928 1,689,014 Dieterle Oct. 23, 1928 1,765,367 Dieterle June 24, 1930 1,848,137 Miller Mar. 8, 1932 1,903,030 Davis Mar. 28, 1933 1,988,493 Hodgson Jan. 22, 1935 

